docs(instrumentation-fastify): deprecate instrumentation in favor of @fastify/otel

[pichlermarc]

Which problem is this PR solving?

Ownership of the instrumentation is moving to https://github.com/fastify/otel. Fastify will provide and maintain an official instrumentation (@fastify/otel) going forward.

See #2647

Short description of the changes

This PR deprecates @opentelemetry/instrumentation-fastify (once merged, I will follow up with deprecation on npm)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.96%. Comparing base (e57f3e4) to head (8bcc68b).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2651      +/-   ##
==========================================
+ Coverage   90.79%   90.96%   +0.17%     
==========================================
  Files         169      172       +3     
  Lines        8061     8137      +76     
  Branches     1646     1649       +3     
==========================================
+ Hits         7319     7402      +83     
+ Misses        742      735       -7     

Files with missing lines	Coverage Δ
...try-instrumentation-fastify/src/instrumentation.ts	95.38% <ø> (ø)

... and 8 files with indirect coverage changes

[trentm]

Suggested change

	This module provides automatic instrumentation for the [`fastify`](https://www.fastify.io/) module, which may be loaded using the [`@opentelemetry/sdk-trace-node`](https://github.com/open-telemetry/opentelemetry-js/tree/main/packages/opentelemetry-sdk-trace-node) package.
	This module provides automatic instrumentation for the [`fastify`](https://www.fastify.dev/) module, which may be loaded using the [`@opentelemetry/sdk-trace-node`](https://github.com/open-telemetry/opentelemetry-js/tree/main/packages/opentelemetry-sdk-trace-node) package.